Hydraulic motors



June 2, 1964 R. A. CLARK 3,135,167

HYDRAULIC MOTORS Filed Sept. 11, 1962 2 Sheets-Sheet l A CUMULATOR TANK Inventor Richard A. Clark,

B Wallac Md Draw flamed/k6 June 2, 1964 Filed Sept. 11, 1962 R. A. CLARK HYDRAULIC MOTORS SEQ 2 Sheets-Sheet 2 TO TANK Zl \l 25 30 2e f f Inventor FROM ACCl-IMO LA OR Richard A. Clark- 33/ w y am /P pq-Htorneqd United States Patent 3,135,167 HYDRAULIC MOTQRS Richard A. Clark, Oxnard, Calif, assiglor to American Brake Shoe Company, New York, N.Y., a corporation 7 of Delaware Filed Sept. 11, 1962, Ser. No. 222,862 2 Claims. (Cl. 91-475) This invention relates to a hydraulic motor, and in particular to a starter motor having means associated therewith for connecting the input pressure port of the motor to the exhaust port at a predetermined speed of the motor, resultantly enabling the motor to coast and thereby preventing damage to the motor that might be engendered by overspeeding.

The hydraulic motor of the present invention can be described from the standpoint of one useful adaptation thereof in connection with jet aircraft. Thus, initial rotation is usually imparted to a jet engine, for starting purposes, by a hydraulic motor, coupled to the jet engine through an over-running clutch. When the speed of the jet engine reaches approximately 6000 rpm, the fuel is ignited and the engine is under its own power, increasing in speed and tending to pull away from the starter motor as enabled by the presence of the over-running clutch.

When the jet engine load is removed from the starter motor, the motor may be overloaded by the hydraulic pressure source, accelerating rapidly to speeds which may cause damage to the motor. The primary object of the present invention is to avoid this condition by associating with the motor a control valve and bypass means effective at a predetermined engine speed to connect the input and exhaust ports of the motor so that fluid from the aceumulator or other source of fluid under pressure will flow to the output or exhaust side of the motor. Resultantly, the pressure source is in direct communication with the tank or reservoir that is connected to the motor output, and the pressure in the accumulator or equivalent is reduced to less than that which will produce excessive speeds in the motor.

Specifically, it is an object of the present invention to accomplish the foregoing by connecting the opposite ends of a normally closed spring-biased valve spool to the upstream and downstream sides of an orifice at the output of the motor. When the output pressure of the motor exceeds the set value of the spring bias, the valve spool is shifted to interconnect the input and output ports of the motor as aforesaid whereby fluid under pressure for driving the motor is bypassed to the tank or reservoir.

Other and further objects of the present invention will be apparent from the following description and claims and are illustrated in the accompanying drawings which, by way of illustration, show a preferred embodiment of the present invention and the principle thereof and what is now considered to be the best mode contemplated for applying that principle. Other embodiments of the invention embodying the same or equivalent principles may be made as desired by those skilled in the art without departing from the present invention and the purview of the appended claims.

In the drawings:

FIG. 1 is a sectional view of a typical motor to which the present invention is applied;

FIG. 2 is an end elevation of the motor shown in FIG. 1, and partly in section; and

FIG. 3 is a schematic drawing illustrating the porting involved under the present invention.

The hydraulic motor illustrated at in FIG. 1 is merely representative of a typical starter motor for a jet engine, fulfilling the purpose discussed above. The motor 10 is of a known kind wherein pistons 11 in a cylinder barrel 12 reciprocate parallel to the axis of the cylinder 3,135,167 Patented June 2, 1964 barrel as an incident to hydraulic fluid under pressure being supplied to the cylinders 13. Torque is imparted to the cylinder barrel 12 as a result of the reactions of the pistons against a cam plate 15 which, incidentally, in FIG. 1 is illustrated out of position.

The cylinder barrel is keyed to a multiple section drive shaft including an end element 17. Hence, the drive shaft is rotated by the cylinder barrel when fluid under pressure is applied to the input of the motor. It may be noted that it is the driven element 17 which is connected to the aforementioned over-running clutch interposed between the motor 10 and the driven member of the jet engine.

Fluid under pressure is supplied from an accumulator, or other suitable source (not shown) to the inlet 20 of the motor 10, and the inlet is connected to a valve plate port 21 past which rotate the cylinders 13 to be charged with fluid under pressure incidental to establishing the torque reactions that are responsible for rotating the barrel 12and drive shaft 17. Again, it should be borne in mind that the cam 15 is 90 out of phase in FIG. 1. Hydraulic fluid is discharged, from the motor to an output 22 which communicates with the valve plate discharge or exhaust port 23.

When the jet engine is to be started, fluid under pressure is admitted from the accumulator to the motor inlet 20, and the entering high pressure fluid is admitted to the cylinders having the pistons therein displaced by the least amount by the cam 15, to drive the motor, as is well known. The pistons exhaust the fluid at the exhaust port 23, this exhaust fluid being forced through the outlet conduit or passageway 22 to the tank or reservoir, not shown.

A motor of the kind illustrated in FIG. 1 can be damaged by overspeeds, as in the instance of suddenly unloading the motor as a starter motor under the circumstances explained above. Thus, at this time the full pressure of the source is applied to the unloaded motor. It therefore becomes important to avoid this condition, and under the present invention overspeeding is avoided by connecting the pressure input 2021 to the discharge line 22 on the upstream side of a restriction or orifice 24 located in the discharge passage 22 as explained in more detail here inafter.

In achieving the foregoing, resort is had to a two-position one-way control valve 25 including a valve spool 26 interposed in a passage or conduit 2829 that interconnects the input of the motor with the exhaust or output 22 as shown in FIG. 3. Thus, the passage 28 leads from the input 20 to the valve 25, and the passage 29 leads from the valve 25 to the output 22 at the upstream side of the orifice 24.

The valve spool 26 is normally in a closed position with respect to the passages 28-29 so that normally motor input and output are not in communication. The valve is held closed by a biasing force exerted as by a spring 3%] adjustable by way of an adjusting screw 31.

As noted above, the discharge passage 22 is restricted at 24 so as to create an upstream-downstream pressure differential thereacross. The upstream pressure is communicated by a port or passage 32 to a chamber 25A at the unbiased end of the valve spool 26. The downstream or low pressure side of the orifice 24 is communicated to the biased end of the valve spool 26 through a passage 33. Moreover, while the ends of the valve spool are of equal area this is not essential, but is preferred for simplicity of manufacture.

Advantageously, the force of the spring 30 versus the area at the unbiased end of the valve spool 26 is such that a predetermined pressure drop, for example, approximately a psi. across the orifice 24 will cause the valve spool to be shifted to a position where the groove 26G thereof is interposed in the passage 28-29 to enable the accumulator to discharge to the exhaust passage 22.

The spring 30 will be preset to apply a biasing force that is overcome by pressure in the passage 32 acting on the valve spool when the motor is operated at a rate representative of overspeeding, as where it is in effect uncoupled from the jet engine which was started by the motor 10. Under this circumstance, the accumulator tends to cause the hydraulic motor to race, but this will be manifest in an increased exhaust pressure in the discharge passage 22 reflected in an increased pressure in the valve pressure chamber 25A. When this is effective to overcome the biasing force of the spring 30, the valve spool is shifted to the left as viewed in FIG. 3, presenting the groove of the spool to the passage 28, allowing the accumulator to discharge to the passage 29 which is connected to the exhaust passage 22 of the motor on the upstream side of the orifice 24. The full volume and pres sure from the accumulator are thus applied to the high pressure side of the orifice or restriction 24. The pressures at the valve plate ports 21 and 23 become equal and the cylinder barrel of the motor is no longer driven. These conditions prevail until the accumulator pressure is discharged to a degree where the pressure differential at the restriction 24 no longer is elfective to hold the valve spool in the open position thereof that establishes communication between passages 28 and 29. The valve 25 will therefore close, but under circumstances where the motor can no longer be driven at excessive speeds.

The primary advantage in communicating the low or downstream pressure at the orifice 24 to the biased end of the valve spool, through the passage 33, is that this cancels or neutralizes all variables such as back pressures and the like. In other words, inclusion of the passage 33 assures that the valve spool 26 will be affected substantially solely by the pressure drop at the restriction apart from erroneous pressure values that may be produced at the upstream side of the restriction 24 by temperature variations, viscosity changes, back pressure in line 22 downstream of the orifice 24 and the like. 7

It will be seen from the foregoing that a starting motor of the hydraulic type is prevented from overspeeding in accordance with the present invention, when the load is uncoupled therefrom, by providing a restriction in the discharge line of the motor and making provision for communicating the eifect of pressure differential thereof to a two-position valve spool normally in a closed position with respect to a bypass line interconnecting the motor discharge and the source of fluid under pressure for operating the motor. When the pressure differential reaches a high level predetermined as manifesting an overspeeding condition, the valve spool is moved to its open position, against the bias force, by communicating the high pressure at the restriction to the free or unbiased end of the valve spool. Hence, while I have illustrated and described a preferred embodiment of the present invention, it will be understood thatthis is capable of variation and modification, and I thereforedo not wish to be limited to the precise details set forth, but desire to avail myself of such changes and alterations as fall within the purview of the following claims.

I claim:

1. In a hydraulic system including a motor driven from a source of fluid under pressure, means for connecting the pressure input of the motor to the exhaust of the motor at a predetermined motor speed, resultantly enabling the motor to coast, comprising passage means interconnecting the motor input and exhaust, a control valve interposed in said passage means and including a valve spool normally biased to a closed position with respect thereto by a bias force of predetermined magnitude applied to one end thereof, the output exhaust of the motor having discharge passage means including a restriction creating an upstream-downstream pressure differential thereacross, and means communicating the high upstream orifice pressure to the unbiased end of said spool and the low downstream orifice pressure to the biased'end of said spool, whereby the bias force is overcome and the valve opened when the pressure on the upstream side of the orifice reaches a specified magnitude characterizing an overspeeding motor.

2. In a hydraulic system including a motor driven from a source of fluid under pressure, means for connecting the pressure input of the motor to the exhaust of the motor at a predetermined motor speed, resultantly connecting the source to discharge and enabling the motor to coast, comprising passage means interconnecting the motor in put and exhaust, a control valve interposed in said passage means and including a valve spool normally biased to a closed position with respect thereto by a bias force of predetermined magnitude applied to one end thereof, the exhaust of the motor having discharge passage means including a restrictioncreating an upstream-downstream pressure differential thereacross, and means communieating the high upstream orifice pressure to the unbiased end of said spool, whereby the bias force is overcome and the valve opened when the pressure on the. upstream side of the orifice reaches a specified magnitude characterizing an overspeeding motor.

References Cited in the file of this patent UNITED STATES PATENTS 2,813,517 Sedwick Nov. 19, 1957 2,989,616 Mironofi June 20, 1961 3,064,426 Furia et al Nov. 20, 1962 FOREIGN PATENTS 1,180,018 France Nov. 15, 1956 

1. IN A HYDRAULIC SYSTEM INCLUDING A MOTOR DRIVEN FROM A SOURCE OF FLUID UNDER PRESSURE, MEANS FOR CONNECTING THE PRESSURE INPUT OF THE MOTOR TO THE EXHAUST OF THE MOTOR AT A PREDETERMINED MOTOR SPEED, RESULTANTLY ENABLING THE MOTOR TO COAST, COMPRISING PASSAGE MEANS INTERCONNECTING THE MOTOR INPUT AND EXHAUST, A CONTROL VALVE INTERPOSED IN SAID PASSAGE MEANS AND INCLUDING A VALVE SPOOL NORMALLY BIASED TO A CLOSED POSITION WITH RESPECT THERETO BY A BIAS FORCE OF PREDETERMINED MAGNITUDE APPLIED TO ONE END THEREOF, THE OUTPUT EXHAUST OF THE MOTOR HAVING DISCHARGE PASSAGE MEANS INCLUDING A RESTRICTION CREATING AN UPSTEAM-DOWNSTREAM PRESSURE DIFFERENTIAL THEREACROSS, AND MEANS COMMUNICATING THE HIGH UPSTREAM ORIFICE PRESSURE TO THE UNBIASED END OF SAID SPOOL AND THE LOW DOWNSTREAM ORIFICE PRESSURE TO THE BIASED END OF SAID SPOOL, WHEREBY THE BIAS FORCE IS OVERCOME AND THE VALVE OPENED WHEN THE PRESSURE ON THE UPSTREAM SIDE OF THE ORIFICE REACHES A SPECIFIED MAGNITUDE CHARACTERIZING AN OVERSPEEDING MOTOR. 